In The Godfather, Part II, Frank Pentangeli is portrayed as having been one of godfather Vito Corleone's (Marlon Brando) most trusted associates. A rift grows between Pentangeli and Michael, however, that eventually results in Pentangeli betraying the family.

Pentangeli's character was conceived in The Godfather, Part II by Coppola and Puzo when actor Richard Castellano did not reprise his role as Clemenza in the sequel. The Pentangeli character took the part in the plot which was originally intended for Clemenza, whose death was to be set anti-parallel to the extended sequence in which the young Vito becomes Clemenza's partner. It also would have continued the sequence in which Michael is responsible for the deaths of his father's relatives and associates in an order reversing the order in which Vito met them (Carlo Rizzi, Tessio, Roth, Clemenza, Fredo).

Near the beginning of the story, Pentangeli approaches Michael to ask for his help in eliminating the Rosato brothers, rivals in New York, who claimed to have been promised territories by Clemenza prior to his death. Michael refuses, however, and orders Pentangeli to do nothing, as he does not want a war to interfere with an upcoming deal with Hyman Roth (Lee Strasberg), who supports the Rosatos. Pentangeli takes this as an insult and leaves in anger. Later that night, Michael narrowly escapes an assassination attempt at his home.

Michael concludes on his own that Roth was behind the assassination attempt. After visiting Florida to seal the deal with Roth, Michael pays an unannounced visit to Pentangeli on Long Island and asks him to help take his revenge. As part of his plan, he insists that Pentangeli capitulate to the Rosato brothers so that Roth will not suspect that Michael is on to him. Pentangeli prefers open warfare against Roth and the Rosatos, but reluctantly obeys Michael's order.

Pentangeli arranges a meeting with the Rosato brothers. Arriving at the meeting place, Pentangeli leaves his bodyguard outside and enters the bar alone. Once inside, Tony Rosato (Danny Aiello) ambushes Pentangeli with a garotte, telling him, "Michael Corleone says hello." A policeman steps inside, and the attack degenerates into a shootout in the street. Pentangeli disappears and is believed to be dead.

Later, at a Senate hearing investigating organized crime and allegations of Michael's criminal activities, Michael learns that the committee intends to call Pentangeli as a surprise witness to contradict Michael's adamant denial that he is a crime boss. Both Pentangeli and Cicci have been in the protective custody of the FBI since the apparent attempt upon his life. Believing that Michael ordered him murdered, Pentangeli provides a sworn statement to investigators that Michael is the head of the most powerful Mafia family in the nation, controls virtually all gambling activity in North America, and has ordered countless murders.

Most damningly, Pentangeli tells investigators that Michael personally killed Captain McCluskey (Sterling Hayden) and Virgil Sollozzo (Al Lettieri), and also began planning a mass slaughter of New York's other Mafia bosses as early as 1950. Cicci has also disclosed this to the FBI. However, he is unable to directly implicate Michael in any criminal activities; due to "buffers" in the Corleone organization he never received orders directly from Michael. In contrast, since Pentangeli was a capo, there is no insulation between Michael and himself. The Senate subcommittee and the FBI thus consider Pentangeli very credible, and are certain that he can corroborate Cicci's testimony and charge Michael with perjury.

While the Committee is in recess, Michael and others look for a way to avoid the perjury charges. Fredo, who had unknowingly conspired with Michael's enemies, informs Michael that the hearing was engineered by Roth as part of his plan to eliminate him from the scene; plus, the committee's lawyer is on Roth's payroll.

Michael knows that Pentangeli's protective custody is too secure to make an attempt on his life before he testifies. Instead, Michael flies Pentangeli's brother, Vincenzo, in from Sicily, and Vincenzo accompanies Michael to the hearing at which Frank is scheduled to testify. Vincenzo and Frank exchange a silent glance before the hearing. Frightened, Frank recants his earlier statements, saying he "told the FBI guys what they wanted to hear," and now claims that the Corleone family is innocent of any wrongdoing, thus perjuring himself before the Senate committee. This testimony catches the Senators completely off-guard and effectively derails the government's case against Michael.

After the hearing, Corleone family consigliereTom Hagen (Robert Duvall) visits Pentangeli in custody. Hagen tells Pentangeli, a history buff, a story about how traitors in ancient Rome could spare their families if they committed suicide; the implication being that Michael will take care of Pentangeli's family if he kills himself. Pentangeli thanks Hagen, returns to his assigned quarters, and slits his wrists while taking a bath.

The finished film leaves unclear exactly what about his brother's presence motivated Pentangeli to change his story. The final film only states that Vincenzo is a powerful and ruthless Mafia chieftain in Sicily.[1]

An early draft of the film's script explains that Vincenzo, shocked that his brother is about to betray the Corleones, attends the hearing to remind Frank that he must not break the Mafia's code of silence, omertà. His brother's presence, as well as the stare they exchange, serves as a threat that if Frank follows through with his planned testimony, retribution will be taken against his children, who are living in Sicily under Vincenzo's guardianship.[2]

^Puzo, Mario and Coppola, Francis Ford. (1973, September 24). THE GODFATHER Part Two, The Internet Movie Script Database"PENTANGELI: Did my brother go back?HAGEN: Yeah, but don't worry.PENTANGELI: He's ten times tougher than me, my brother. He's old-fashioned.HAGEN: Yeah. He wouldn't even go out to dinner. Just wanted to go home.PENTANGELI: That's my brother. Nothing could get him away from that two mule town. He coulda been big over here — he coulda had his own Family."

^Puzo, Mario and Coppola, Francis Ford. (1973, September 24). THE GODFATHER Part Two, The Internet Movie Script Database"MICHAEL: He said his girlfriend made a spaghetti sauce once and it was so terrible he knew he could never marry her. He set her up in a house in Jersey. She had to be faithful and she had to have kids. And she did. Two, a boy and a girl. He had her checked out and watched so she couldn't cheat but the girl couldn't stand that kind of life. She begged him to let her go. He did. He gave her money and made her give up the kids. Then Frankie took them to Italy and had them brought up by his brother Vincenzo. Where he knew they'd be safe.(Kay begins to realize.)MICHAEL:: When he saw his brother in the hearing room, he knew what was at stake. (pause) I don't think Vincenzo would have done it. He loves the kids, too. Omertà, Kay. Honor, silence."